1. Field of the Invention
The present invention is related to the field of steganography, and more specifically to techniques for embedding owner tracking data in still images and video in a manner that is difficult to detect.
2. Description of the Related Art
The digital representation of data has advanced the efficient and widespread distribution of information, which is generally desirable. However, the facile access to data also presents an increased opportunity for piracy of artistic works, without compensating the owner. Accordingly, methods are being invented for the owners to embed special data in the digital form of the artistic works. This special data, also known as owner tracking data or simply tracking data, corresponds to a signature of the owner. Once embedded in an artistic work, the tracking data can be used to track distribution of all copies of the artistic work.
The techniques for adding tracking data are also known as digital watermarking. A challenge that all such techniques face is that tracking data must be resistant to processing of the image. Such processes include channel noise, copying, filtering, resampling, cropping, lossy compression, resizing, digital to analog and analog to digital conversion. Some of these processes are usual in the ordinary course of treatment of video, whereas others may be intentional so as to remove the tracking data.
A problem in the prior art techniques is that the addition of owner tracking data alters the image. This not only annoys the viewer, but also alerts a prospective pirate as to the very existence of the tracking data.
The present invention overcomes these problems and limitations of the prior art.
Generally, the present invention provides a method for embedding tracking data into graphics data that represents the image according to a first colorspace. The tracking data is embedded during encoding in host locations of the image that have a special host color. While these host locations map properly in the host color in a second colorspace without truncation, the tracking data maps into a blind space of the second colorspace. This does not alter the eventual visual image, which does not alerted the viewer to the presence of tracking data, while it makes it easy to extract the tracking data.
One encoding embodiment is to embed tracking data in the chrominance component of a signal, in locations of the image that are detected to have the host color of black and/or white. Detection of the image color is advantageously performed by examining the corresponding luminance component of the signal. The method is exceedingly resistant to ordinary image processing, because the black and white colors are generally not affected by the image processes.
The present invention results in simple rules for selecting host image areas, for encoding the data, and for extracting it either from the bitstream or from the decoded YCbCr image. The resulting bitstream is compliant with standard decoders. A large amount of user tracking data can be embedded in a given image, up to hundreds of bits of data in a single macro-block. The scheme of the invention also permits the efficient insertion of a small amount of tracking data.
The invention also includes corresponding methods for decoding graphics data so as to extract tracking data. The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the drawings.